Medical professionals and technicians often prepare biological specimens on a specimen carrier, such as a slide, and review the specimens to analyze whether a patient has or may have a particular medical condition or disease. For example, a biological specimen, such as a cytological specimen, is examined to detect malignant or pre-malignant cells as part of a Papanicolaou (Pap) smear test and other cancer detection tests. After a specimen slide has been prepared, automated systems are used to focus the technician's attention on the most pertinent cells or groups of cells, while discarding less relevant cells from further review.
Referring to FIG. 1, one known automated slide preparation system includes a container or vial 10 that holds a biological specimen 12, a filter 20, a valve 30 and a fixed volume vacuum chamber 40. The specimen 12 typically includes multiple cells 14 that are dispersed within a liquid, solution or transport medium 16, such as PreserveCyt, available from Cytyc Corporation (www.cytyc.com). One end of the filter 20 is disposed in the liquid 16, and the other end of the filter 16 is coupled through the valve 30 to the fixed volume vacuum chamber 40. When the valve 30 is opened, vacuum or negative pressure 42 from the fixed volume vacuum chamber 40 is applied to the filter 20 which, in turn, draws or sips liquid 16 up into the filter 20. Cells in the drawn liquid are collected by face or bottom of the filter 20.
It is desirable to collect a sufficient number of cells on the filter to provide a sampling of cells with desired distribution and (limited) thickness. Collecting too many cells can complicate subsequent viewing of the collected by a cytotechnologist or by an inspection or imaging system. For example, cells may crowd other cells and can be stacked on top of each other. This may cause selected cells to be hidden or overlooked when they should have been reviewed. On the other hand, inadequate filter coverage may result in incomplete or inaccurate results, which may also result in cells that should have been reviewed not being collected and reviewed at all.
With the known system shown in FIG. 1, however, collecting the desired number of cells is not as easy as simply turning the valve 30 and applying a vacuum 42 from the fixed volume vacuum source. Rather, multiple iterations of opening and closing the valve and re-evacuating the fixed volume vacuum chamber must be performed.
More particularly, referring to FIG. 2, the cell collection process typically begins by evacuating the fixed volume vacuum chamber 40, if it is not already evacuated, to a suitable negative pressure level. The valve 30 is then opened to apply a vacuum 42 from the chamber 40 to the filter 20 to collect cells 14 against the filter 20. Since the vacuum chamber 40 is a fixed volume vacuum chamber, the vacuum level decreases as cells 14 are collected. The rate of decay of the vacuum level in the vacuum chamber is monitored using a vacuum level indicator 44 or other suitable device over time. The rate of decay of the vacuum level in the chamber 40 is used to indicate the amount of cell coverage on the filter 20. The vacuum level decays faster when the filter has no cells or only a few cells compared to when the filter has collected a larger number of cells.
A determination is made whether or not the filter has sufficient cell coverage based on whether the rate of vacuum decay drops to a certain value from the maximum initial value. During the initial application of vacuum 42, cells 14 are collected by the filter 20. However, the quantity of cells collected usually is not sufficient. Consequently, vacuum 42 must be applied again to the filter 20 to collect additional cells 14.
However, since the vacuum chamber 40 is a fixed volume vacuum chamber and was already evacuated, the vacuum chamber 40 must be re-evacuated. Thus, after each time cells 14 are collected, the valve 30 is closed, the fixed volume vacuum chamber 40 is re-evacuated in order to provide a vacuum environment, and the valve 30 is opened to apply vacuum 42 to the filter 20 to collect additional cells 14. These steps are repeated until the rate at which the vacuum level decays in the fixed volume vacuum chamber drops to a certain level to indicate that sufficient cells 14 have been collected to provide sufficient filter 20 coverage. It may be necessary to repeat these steps many times, e.g., as many as 12-24 times, in order to obtain the desired amount of filter coverage. These steps can require substantial processing time, e.g., 30 seconds, which can quickly multiply to result in processing inefficiencies as more slides are prepared.
In addition to longer processing and preparation times, known systems also typically use a more complicated valve 30. Since the valve 30 is opened and closed so many times, it is desirable and/or necessary that the valve 30 be able to open and close quickly to reduce processing times. Thus, the valve 30 that is used in known systems is often referred to as a “Quick Turn Open” valve or “QTO” valve, as shown in FIG. 1. QTO valves are typically more expensive than other valves, thereby increasing the cost of slide preparation systems.
While known systems and methods have allowed cytotechnologists to effectively prepare slides for subsequent analysis, they can be improved. It would be advantageous to provide a more cost and time efficient slide processing system. It would also be desirable to eliminate repetitive iterations of opening a valve, measuring the decay rate of vacuum within the fixed volume vacuum chamber, closing the valve, and re-evacuating the vacuum chamber until sufficient cells have been collected. Doing so would significantly decrease processing and slide preparation times. Further, it would be advantageous to eliminate the QTO valve, since this valve can be relatively expensive to provide and maintain.